MORPHOLOGICAL-CHANGES IN EXTERNAL AND INTERNAL FEEDING STRUCTURES DURING THE TRANSITION PHYLLOSOMA-PUERULUS-JUVENILE IN THE WESTERN ROCK-LOBSTER (PANULIRUS-CYGNUS, DECAPODA, PALINURIDAE)

External and internal feeding structures of the pelagic final phylloso ma, the transitional puerulus, and the benthic juvenile Western Rock L obster, Panulirus cygnus, were studied by means of scanning electron m icroscopy. The study revealed that the external feeding structures of phyllosomata are well equipped for capture and mastication of food. Th e foregut, however, is not clearly divided into pyloric and cardiac re gions and a gastric mill is absent, although a comb row and gland filt er are present. Juveniles, on the other hand, have a well-developed ga stric mill and gastric teeth, and a cardiopyloric valve separates the foregut into cardiac and pyloric regions. External mouthparts of juven iles are suitable for mastication of solid food particles and bear num erous setae. In contrast, external mouthparts of pueruli are largely n on-setose. Furthermore, although the foregut is differentiated into py loric and gastric regions and a gland filter and comb row are present, a functional gastric mill is absent during the puerulus stage. Absenc e of such structures indicates that the puerulus may be a non-feeding stage. It is postulated that absence of (or reduced) feeding may be a response to an increased risk of predation rather than a result of the considerable morphological changes taking place during the transition from a planktonic to a benthic lifestyle, as has been previously prop osed. (C) 1994 Wiley-Liss, Inc.